This invention relates to the production of high purity glucose syrups directly from starch.
Crystalline dextrose or glucose is an essentially pure product, e.g. 99.5+% purity, and is of wide spread food and industrial usage. Manifestly some uses for dextrose, including for example preparation of intravenous feeding glucose solutions, require a dextrose of utmost purity. For many uses, including for example employment as the starting material for manufacture of sorbitol, and as the dextrose supplement in fermentation media, minor impurity levels can be tolerated and dextrose of purity levels exceeding 98% would be quite adequate. Nonetheless, crystalline dextrose is employed for such uses, likely because heretofor the art has not provided any satisfactory alternative to crystalline dextrose. The art has been able to offer in large quantities, either crystalline dextrose or a (glucose) syrup containing something less than about 95% purity dextrose on a dry weight basis, and 95% purity is considered inadequate for many dextrose uses.
The less than 95% purity level of the glucose syrups available until the recent development of enzymatic starch liquefaction procedures encouraged many potential syrup users to employ crystalline dextrose creating a strong tendency for continued use of crystalline dextrose in face of the availability of 98 DE syrups (which represents a purity level of about 97%). Little or no substitution of glucose syrup for crystalline dextrose can be forseen until 98% or purer glucose syrup can be made available.
Historically (corn) starch has been converted to high DE glucose syrups by heating an acidified starch slurry which liquefies the starch and thereafter enzymatically saccharifying the liquefied starch (or dextrin) solution to a high DE level. Side reactions during liquefaction and during saacharification create polysaacharide impurities. Purification of the syrup by carbon treatment and by ion exchange treatment will remove noncarbohydrate impurities, but polysaacharide impurities remain in the syrup. The best glucose (or dextrose) purity levels achieved in industrial practice is believed to be about 95 DE. Substitution of a combination acid/(alpha-amylase) enzyme starch liquefaction procedure for the acid liquefaction can result in glucose syrup purity levels of about 97 DE. Careful enzymatic liquefaction results in a further purity improvement, but only to about 98 DE. Manifestly, further purity improvement of any real significance can come only by coupling the best known starch liquefaction procedure to a superior saacharification procedure.